Irrigation systems utilize a series of pipes or conduits for conveying water from a water source to a series or network of water emitters or sprinklers. Though at one time metallic pipes were used, these suffered from exterior rust and corrosion, as well as interior fouling, and carried a high materials expense. Coatings were developed which promoted the life of metallic pipes, and the use of large diameter pipes helped alleviate the problems with interior fouling. However, cost remained an issue until polymeric piping was developed.
Polymer or plastic piping offered additional benefits. For instance, threading and sealing of plastic joints is simpler and more reliable. One drawback to plastic piping has traditionally been its strength, particularly in localized regions containing stress concentrators or non-uniform mechanical properties.
A common irrigation component is a sprinkler utilizing a pop-up spray head. This type often includes a deflector plate secured to a base assembly coupled to a riser or other tube. The riser is received within a sprinkler body that is typically stationary and buried in the ground with a generally vertical orientation. In this manner, the riser and spray head may move between an extended and elevated position relative to a sprinkler body and a retracted and lower position where the riser is substantially received within the sprinkler body. When extended, the spray head is positioned above the ground level to water the surrounding area.
The length of the sprinkler body is typically dependent on the riser length. That is, a typical sprinkler body with a length of 4 inches may be coupled with a riser having a length of 2 inches, while another sprinkler body of 16 inches may be used with a 12 inch riser. In relatively shorter forms of the sprinkler body, the water may be received from the water source at a lower end of the sprinkler body. However, relatively longer forms for the sprinkler body usually require a side inlet. This may also vary depending on the irrigation application.
Though much plastic piping can be formed as a continuous length by extrusion, for instance, other components to the irrigation system are made by injection molding. Injection molding often leads to non-uniform mechanical properties, such as a weakened point or weakening feature referred to as a knit line. Specifically, thermoplastic polymers flow at a rate dependent on their temperature. The polymeric materials are typically forced into a mold with a temperature lower than that of the plastic. Therefore, the plastic begins to cool on contact. This cooling is most pronounced at the leading edge of the injection flow, and the leading edge begins to solidify and develop a surface texture as it flows through the mold. When two leading edges meet, a visible line referred to as a knit or mold line is formed. It is known that the plastic material localized at the knit line does not tend to form as strong a bond because the polymer strands do not join and flow as well. Therefore, the knit line does not bond as well and tends to be more brittle. Though the sprinkler bodies maybe reinforced with fibers such as fiberglass, these fibers do not often cross the knit line weld interface, so the knit line does not realize the benefits of the presence of the fibers. Therefore, the knit line typically weakens the piping.
One example of a component made with such a process is the sprinkler body having a side inlet. Because the geometry of a sprinkler body does not lend itself to extrusion molding, injection molding tends to be more practical to construct the body and the side inlet, as well as a short cylindrical wall that typically surrounds the inlet. From a manufacturing standpoint, principal injection techniques for forming such a sprinkler body often result in the knit line being coincident with or bisecting the side inlet and the cylindrical wall.
In service, it is not uncommon for the sprinkler body to be filled with water even when the spray head is not presently emitting water. Prior to an off season, the sprinkler is cleared with air so that water does not freeze within the system, which would otherwise cause potentially catastrophic damage. Otherwise, in the absence of some type of bleed control for releasing pressure, the sprinkler body contains a full, static volume of water. In order to activate the sprinkler, the water source is opened such that a pressure surge is applied to the system, thereby forcing water through the system, raising the pop-up heads, and allowing water to be emitted.
The maximum stress is experienced when the pressure surge is transmitted to the full sprinkler body. That is, the pressure directed through the sprinkler body is not free to simply pass through as the standing water in the sprinkler body must be energized to overcome its static state. This creates the highest stress on the sprinkler body. The location of the maximum stress when such a pressure surge is transmitted is the stress concentrators of the sprinkler body. More specifically, the highest stress concentrator is the knit line bisecting the side inlet and the cylindrical wall.
One method for examining the strength and durability of a sprinkler body is by repeatedly recreating these conditions. Known as cycle-surge durability testing, a plugged, water-filled sprinkler body is subjected to a series of repeated high-pressure surges at levels often in excess of conditions typically used by a consumer. This allows for recognizing long-term performance deficiencies. In performing such tests, it has been found that sprinkler bodies with a side inlet underperform bodies without a side inlet. More particularly, the side-inlet sprinkler body often fails by rupturing proximate the side inlet and along the knit line.
Accordingly, it is desired for a side-inlet sprinkler body having improved performance and structural integrity.